This invention relates generally to cable racks which are used to support heavy cables and splice cases in manholes and controlled environmental vaults. More particularly, the present invention relates to various devices and techniques for bonding the cable racks to a common ground point.
Cable racks to which the invention relates are commonly installed in manholes and controlled environmental vaults. The cable racks conventionally are elongated metal members which are vertically oriented and bolted to concrete walls by lag bolts or other conventional fastening means. T-slotted racks have a single elongated mounting surface having a row of T-shaped openings. The Unistrut P16F(trademark) and P21H(trademark) racks are elongated tubes having a substantially square cross-section. One set of opposed sides have a row of rectangular-shaped openings and the other set of opposed sides have a row of oval-shaped openings. Hooks for supporting heavy cables, splice cases and other products are removably installed upon insertion in the cable rack openings.
The cable rack environment is frequently subject to ground water contamination as well as significant quantities of corrosive compounds. Salt and other corrosive chemicals are also found in the ground water. Consequently, the ground water functions as an electrolytic solution relative to the racks. If the metal hardware of the cable racking in the controlled environmental vaults or manholes is not at the same electrical potential, the electrolytic system accelerates corrosion of the cable racks.
The tendency of the metal cable racks to corrode as a result of their presence in an electrolytic system, has dictated the common practice of connecting the cable racks to a common ground point. The conductor connection with a common ground point is commonly accomplished in a wide variety of on-site expediently devised techniques, the most common technique is simply to clamp the ground conductor between a pair of washers secured to a lag bolt which mounts the cable rack.
U.S. Pat. No. 5,094,622 discloses a bond clamp which attaches to a T-slotted cable rack for connecting a ground conductor. An L-shaped bolt is inserted in the T-slot to secure a pair of clamp members to the cable rack. The ground conductor is clamped 10 between the clamp members to provide the electrical bond connection with the cable rack. The base clamp members includes a pair of laterally extending guide flanges such that the base clamp member substantially encloses the front face and side portions of the T-slotted cable rack. Since commercially available T-slotted cable racks is narrower than the Unistrut racks, the guide flanges prevent use of these bond clamps on Unistrut racks.
Briefly stated, the invention in a preferred form is a cable rack clamp which comprises a clamping member composed of a corrosion-resistant, electrically conductive material. The clamping member includes a longitudinally extending, U-shaped female mounting segment having a front wall and oppositely disposed side walls. A clamping segment extends laterally from the side walls at an end portion of the female mounting segment. The clamping segment and front wall and side walls of the end portion define an opening. A base member composed of a corrosion-resistant electrically conductive material includes upper, lower and male mounting segments. The male mounting segment is dimensioned to be slidably received in the opening of the clamping member. A retainer composed of a corrosion-resistant, electrically conductive material may be inserted through the opening of the cable rack. A first bolt composed of a corrosion-resistant, electrically conductive material mounts the retainer to the base member and may be torqued to exert a clamping force between the retainer and the base member, whereby the retainer and the base member engage opposed sides of the rack to clamp the base member thereto. A second bolt composed of a corrosion-resistant, electrically conductive material mounts the clamping member to the base member and may be torqued to exert a clamping force between the clamping member and the base member. Ground conductors disposed between the either first bolt and the base member or between the clamping segment of the clamping member and the lower segment of the base member are clamped therebetween.
The first and second bolts each include a head, a threaded shaft and a flange of disposed intermediate the head and the threaded shaft. The flange of the first bolt is disposed adjacent the front surface of the base member, with the threaded shaft extending through the opening of the base member and engaging the threaded opening of the retainer. The diameter of the opening of the base member is greater than the outside diameter of the shaft, such that the shaft moves freely within the opening. The flange of the second bolt is disposed adjacent to the clamping member, with the threaded shaft extending through the opening of the clamping member to engage a longitudinally extending threaded bore of the male mounting segment.
The male mounting segment of the base member includes a pair of side surfaces, each having a longitudinally extending groove. Each of the side walls of the female mounting segment of the clamping member has a longitudinally extending ridge which is received in each of one of the grooves of the base member. The distance between the side walls is greater than the width of the male mounting segment, the height of the ridges is complimentary to the depth of the ridges, and the width of the grooves is greater than the thickness of the ridges.
The retainer has upper and lower portions, with the upper portion of the retainer extending laterally forward of the lower portion to form a shoulder. The shoulder of the retainer is supported on the lip of the opening of the cable rack.
It is an object of the invention to provide a new and improved ground clamp for electrically bonding a ground conductor to a cable rack.
It is also an object of the invention to provide a new and improved ground clamp specifically adapted for mounting to a cable rack to provide a ground connection of high integrity.
A further object of the invention is to provide a new and improved ground clamp for efficiently electrically bonding a wide variety of ground conductors to either a T-slotted cable rack or a Unistrut cable rack.
Other objects and advantages of the invention will become apparent from the drawings and specification.